Re: [PATCH] hwmon: (max6639) : Allow setting target RPM

From: Guenter Roeck
Date: Mon Mar 24 2025 - 19:30:23 EST


On 3/24/25 11:57, Your Name wrote:
From: Naresh Solanki <naresh.solanki@xxxxxxxxxxxxx>

Currently, during startup, the fan is set to its maximum RPM by default,
which may not be suitable for all use cases.
This patch introduces support for specifying a target RPM via the Device
Tree property "target-rpm".

Changes:
- Added `target_rpm` field to `max6639_data` structure to store the
target RPM for each fan channel.
- Modified `max6639_probe_child_from_dt()` to read the `"target-rpm"`
property from the Device Tree and set `target_rpm` accordingly.
- Updated `max6639_init_client()` to use `target_rpm` to compute the
initial PWM duty cycle instead of defaulting to full speed (120/120).

Behavior:
- If `"target-rpm"` is specified, the fan speed is set accordingly.
- If `"target-rpm"` is not specified, the previous behavior (full speed
at startup) is retained.


Unless I am missing something, that is not really correct. See below.

This allows better control over fan speed during system initialization.

Signed-off-by: Naresh Solanki <naresh.solanki@xxxxxxxxxxxxx>
---
drivers/hwmon/max6639.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/max6639.c b/drivers/hwmon/max6639.c
index 32b4d54b2076..ca8a8f58d133 100644
--- a/drivers/hwmon/max6639.c
+++ b/drivers/hwmon/max6639.c
@@ -80,6 +80,7 @@ struct max6639_data {
/* Register values initialized only once */
u8 ppr[MAX6639_NUM_CHANNELS]; /* Pulses per rotation 0..3 for 1..4 ppr */
u8 rpm_range[MAX6639_NUM_CHANNELS]; /* Index in above rpm_ranges table */
+ u32 target_rpm[MAX6639_NUM_CHANNELS];
/* Optional regulator for FAN supply */
struct regulator *reg;
@@ -560,8 +561,14 @@ static int max6639_probe_child_from_dt(struct i2c_client *client,
}

target_rpm[] is 0 here.

err = of_property_read_u32(child, "max-rpm", &val);
- if (!err)
+ if (!err) {
data->rpm_range[i] = rpm_range_to_reg(val);
+ data->target_rpm[i] = val;
+ }

If there is no max-rpm property, or if there is no devicetree support,
target_rpm[i] is still 0.

+
+ err = of_property_read_u32(child, "target-rpm", &val);
+ if (!err)
+ data->target_rpm[i] = val;

If there is neither max-rpm nor target-rpm, target_rpm[i] is still 0.

return 0;
}
@@ -573,6 +580,7 @@ static int max6639_init_client(struct i2c_client *client,
const struct device_node *np = dev->of_node;
struct device_node *child;
int i, err;
+ u8 target_duty;
/* Reset chip to default values, see below for GCONFIG setup */
err = regmap_write(data->regmap, MAX6639_REG_GCONFIG, MAX6639_GCONFIG_POR);
@@ -639,8 +647,9 @@ static int max6639_init_client(struct i2c_client *client,
if (err)
return err;
- /* PWM 120/120 (i.e. 100%) */
- err = regmap_write(data->regmap, MAX6639_REG_TARGTDUTY(i), 120);
+ /* Set PWM based on target RPM if specified */
+ target_duty = 120 * data->target_rpm[i] / rpm_ranges[data->rpm_range[i]];

If there is no devicetree support, or if neither max-rpm nor target-rpm are
provided, target_duty will be 0, and the fans will stop.

Maybe my interpretation is wrong, but I think both target_rpm[] and rpm_range[]
will need to be initialized. Also, it seems to me that there will need to be an
upper bound for target_rpm[]; without it, it is possible that target_duty > 120,
which would probably not be a good idea.

Guenter

+ err = regmap_write(data->regmap, MAX6639_REG_TARGTDUTY(i), target_duty);
if (err)
return err;
}

base-commit: 2115cbeec8a3ccc69e3b7ecdf97b4472b0829cfc